Process for the purification of rolling mill oil



Aug. 9, 1966 R. T. BONSALL, JR

PROCESS FOR THE PURIFICATION OF ROLLING MILL OIL Filed May 9, 1965 R L Hm m m m T A & Y v25 G at; EMI M R QEP mmmma .rmmIm United States Patent'Rodney T. Bonsall, .lrn, Philadelphia, Pa, assignor to PennsaltChemicals Corporation, a corporation of Pennsylvania lFiled May 9, 1963,Ser. No. 279,098 3 Claims. (Cl. 210-73) This invention relates to aprocess for the purification of rolling mill oil. More specifically,this invention relates to the removal from rolling mill oil of millcoolant water, tramp oil, and insoluble impurities, such as dirt, dust,iron oxide and carbon.

In the manufacture of continuous sheet steel or other metals, it isconventional to cold roll a continuous strip of the metal by passing itthrough a series of press rolls, each pair of rolls pressing the stripinto a longer, thinner sheet. By such an operation steel sheet having athickness of .003 to .004" may be produced, the end product beinguseful, for instance, in the fabrication of tin cans. To cut down thefriction involved in the rolling operation, to avoid sticking, to avoidheat build-up, and to carry off oxides and dust, it has been customaryto spray the metal entering the nip of each pair of rolls with anexpensive compounded lubricating or rolling oil. To further cool theoperation in a so-called direct application procedure, the thinner sheetemerging from the rollers is sprayed with large quantities of water.

It has been customary as shown in the prior art to collect the mixtureof rolling oil and coolant water in a pit or trough underneath the pressrolls and convey it to a settling tank, the lighter oil subsequentlybeing pumped off and returned to the mill for reuse. The settled waterhas also been reused or in situations in which water has been inplentiful supply has been discarded. A prior art example of such aprocess is disclosed in Patent 2,140,289 to Hurtt et al., which issuedDecember 13, 1938.

A heretofore unavoidable problem connected with such clarification hasbeen the leakage into the system of relatively small quantities of trampoil. Tramp oil is a generic name applied to oil used to lubricate thebearings of the press roll and also used in the pressure cylinders ofthe rolls. The tramp oil, invariably of a petroleum base, has found itsway into the rolling oil-coolant water system, usually by simplydropping downward into the pit or trough beneath the rolls. Being oflight weight it has in the past settled with the rolling oil and hasbeen withdrawn with the rolling oil and returned to the mill for reuse.The tramp oil is itself dark in color and in contact with dirt, etc. inthe rolling operation becomes darker with each reuse. As a consequencetramp oil applied with the rolling oil has caused blotches and stainsand imperfections on the surface of the sheet product.

Rather than risk a poor product, metal processors have been forced tocompletely dispose of their rolling oil at frequent intervals and havereplenished the system with fresh oil at great expense.

In addition to contamination with tramp oil, the rolling oil will aftera short period of use contain the usual insoluble contaminantsdirt,dust, iron oxide and carbon-the presence of which is serious and to beavoided. A portion of the insoluble contaminants are of such size thatthey are easily settled in the pit and removed from the system assludge. On the other hand some of the solids are fine and heretoforehave been virtually impossible to remove.

It is a feature of the present invention to remove portions of the trampoil and keep its presence in the rolling ice mill system down within atolerable limit without undue loss of rolling oil.

It is a further feature of this invention to remove from the rollingmill system fine insolubles which are difiicult to settle and whichotherwise would be returned to the rolls with the rolling oil.

Other features of the invention will be apparent to those skilled in theart upon reference to the following description of a preferredembodiment of the invention, with further reference to the drawing whichis a diagrammatic perspective view of a process embodying the invention.

As represented diagrammatically in the figure, at the sheet press anumber of pairs or stands of cooperating rolls work successively on thesheet. Each pair of rolls may comprise a bottom or back-up rollpositioned under the sheet and an upper roll or work roll pressed towardthe lower roll by a hydraulic ram to develop pressure against the sheetbetween the rolls. The rolls, of course, are mounted on bearings whichare provided with lubrication by means not shown. The lubricating oilfrom the bearings and the hydraulic fluid from the rams comprise thesource of tramp oil with which the invention is concerned. As alsoindicated diagrammatically in the figure roller oil is sprayed againstthe sheet as it enters the nip of each pair of rolls. Coolant water issprayed as the sheet emerges from each pair.

Positioned below the press is a rectangular pit adapted to collect theused rolling oil, the mill coolant water, insolubles and the tramp oil.In actual installation such a pit is of ample area to underlie allportions of the operation from which the above-mentioned liquids mayfall and thus serves effectively to collect them.

As shown in the figure the mixture of rolling oil, mill coolant waterand tramp oil is conducted from the pit to a large settling tank (forinstance, of 10,000 gallon capacity) and it is in this settling tankthat the collection commences to settle in accordance with the specificgravity of its various portions. For instance at the lower end of thetank the heavy solids will accumulate so that they may be drained andlet off as the sludge discharge from the system. Above the sludge in thesettling tank will be an indefinite layer of coolant water emulsifiedwith the rolling oil, the proportion of oil becoming greater as the topof the tank is approached. Throughout the emulsion there will be finesolids which because of their small size are slow in settling. Adjacentthe top of the settling tank collection will be a layer of rolling oilwhich has not 'been emulsified with the coolant water.

After the collection 'has been allowed to remain in the tank undisturbedfor some time after start-up (for instance 30 minutes) the centrifugalseparation of the collection into its various components may commenceand may operate on a continuous basis thereafter. As shown, liquid froma point A adjacent the lower end of the settling tank but above thesludge layer is drawn olf, passed by a pair of vents at B to permitescape of entrapped gases and pumped along wit-h portions of the sludgedischarge if necessary or desired to a pair of centrifuges C and Ddisposed in.- parallel. This liquid may comprise, for instance, 15% oiland water.

Centrifuges C and D are similar, both being of the type comprising asolid bowl having periphenal nozzles and a pair of coaxial ring damsover which the lighter oil and the heavier water discharge respectively.Such centrifuges are available from The Sharples Corporation under thetrademark Nozljector centrifuge. Each of the centrifuges preferablycontains a stack of frusto-conical discs within which the interfacebetween the two liquids, oil and Water, is appropriately maintained.Thus the zone of greatest separating efficiency, the disc stack,

Works the most difiicult portion of the stubborn emulsion, breaks it andseparates it into its two components. As shown the ring dam dischargesfrom the centrifuges C and D are respectively collected together in awater catch tank which collects the liquid from the outer ring dam ofeach machine and provides a water discharge for the entire system; andan oil catch tank collects the inner ring darn discharges. For greatestelficiency in the process the position of the interface within themachines C and D is controlled so that the water discharge is virtuallyfree of any oil while the oil discharge may have some degree of wetness.In other words, at this stage in the process the concern is more indischarging an oil- -free water than a water-free oil.

The nozzle discharge of the centrifuges C and D is solids and water andis collected in the sludge box shown at the right-hand side of thefigure and settled prior to disposal.

From the oil catch tank liquid is pumped as shown to a surge tank. Alsodelivered to the surge tank is a discharge from a point B adjacent theupper end of the settling tank and containing rolling oil in which thereis a lesser degree of water than might be found in the emulsion at alower point in the settling tank. From E, for instance, the drawoff maybe 15% water and 85% rolling oil.

From the surge tank the flow which is rolling oil with small amounts ofwater is conducted to a centrifuge F. In the preferred form of theinvention centrifuge F is in the form of a solid wall centrifuge havingperipheral nozzles and a single ring dam discharge from which theclarified rolling oil may discharge. Also provided in the centrifuge isan underflow arrangement by which a supplemental liquid may be deliveredto the inside of the bowl adjacent the peripheral wall. Such acentrifuge is thoroughly disclosed in the US. Patent 3,047,214 whichissued July 31, 1962 on an application by Francis P. Downing. In thepresent process the underfiow is provided from a recycle tank as shownto which is deli-vered the nozzle discharge of centrifuge F. The nozzledischarge will contain, of course, a high percentage of water With somesolids and it is part of this water which is returned to the machine asunderflow to satisfy the demands of the centrifuge nozzle or peripheralopenings without permitting passage therethrough of the lighter rollingoil. It is by this means that the interface between the aqueous androlling oil phases may be located adjacent the periphery of thecentrifuge bowl outside the disc stack without danger of losing thevaluable rolling oil to the aqueous nozzle discharge. Such a machinewhich greatly accounts for the efficiency of the process is availablefrom The Sharples Corporation under the trademark Gravitrol centrifuge.

The ring dam discharge from the centrifuge F is delivered to a clarifiedoil catch tank and is drawn off to comprise the clean rolling oildischarge for the system. It is returned to the press and reapplied tothe sheet as it enters each pair of rolls.

As shown, the recycle tank includes an upward vertical partition G overwhich the lightest layer may fall into a separate compartment H. Thewater from the larger compartment of the recycle tank is not onlydelivered back to centrifuge F to satisfy the nozzles, but also aportion of this water is delivered back to the settling tank at a pointI preferably intermediate points A and E for reprocessing. This water,since it comes from a point I spaced above the bottom wall of therecycle tank, may contain some oil.

From adjacent the bottom wall of the compartment H of the recycle tankthe liquid which overflowed the partition G is led off. This liquid,upon analysis, contains to a large percentage tramp oil which as notedabove originated from the bearing and hydraulic leakage for the press.The tramp oil discharge not only contains a high percentage of theundesired tramp oil but many of the fine solids which appeared throughthe settling tank. The tramp oil discharge together with the solids offine size may be sent to disposal.

The appearance of the tramp oil in the recycle tank is surprising. Onewould expect that having once mixed with the rolling oil of the mill itcould not be separated thereform under any circumstances. However, itconsistently appears in the heavy discharge from the centri fuge F andin an actual installation the output of rolling oil has reached anequilibrium with only 1% tramp oil contamination. This small amount ofcontamination is entirely tolerable to the processor.

The reason for the appearance of the tramp oil with the aqueousdischarge from the centrifuge F is not known. It is believed, however,that the tramp oil being mineral-based is not soluble in the normallyfatty-oilcontaining rolling oil-coolant water emulsion which it meetsduring the rolling operation. Being an oil-phase the tramp oil moves into selectively wet the finer insolubles in the system and to comprisewhat may be regarded as a lighter solids phase. This solids phase, asdistinguished from the rolling oil--mill coolant light emulsion whichbehaves like an aqueous phase, retains its identity and during the finalclarification moves out with the water in a split off from the rollingoil.

A rolling oil may comprise a preponderance of fattybased oils withvirtually no petroleum distillates. Alternatively, rolling oil maycomprise a mixture containing 50% of a petroleum distillate with theremaining portion a mixture of fatty-based oil such as palmic and anonionic emulsifier. The emulsifier gives to the mixture the qualitiesof a homogeneous phase. Tramp oil, on the other hand, as stated, is apetroleum-based product.

Other explanations for the success of the system are possible. It issufiicient to acknowledge, however, that by the arrangement of theinvention the amount of tramp Oil returned to the mill may be keptwithin tolerable limits. Just as important, with the tramp oil areremoved insoluble impurities. These impurities would otherwise bereturned to the mill and ultimately affect the quality of the millproduct.

It should be understood that reasonable variations from the processshown are contemplated within the limits of the appended claims. Wherepumps are shown in the drawings, simple gravity delivery or other meansof conveyance may be substituted. Further, the use of a singlecentrifuge of the same or comparable type may be made in place of theparallel centrifuges C and D. Also to facilitate the initialstratification which takes place in the settling tank as shown, simplecyclones may be employed, for instance, as a pair in series with thelight discharge of the first cyclone comprising the discharge E and theheavy discharge being delivered under pressure to the second cyclonealong with recycle which appears at point I in the figure. The lightdischarge from the second centrifuge may comprise the discharge found atpoint A in the figure While the heavy discharge may be the bottom sludgedischarge of the settling tank. Thus many variations of the preferredprocess are possible.

In orther words, having particularly described the invention, it is tobe understood that this is by way of illustration, and that changes,omissions, additions, substitutions, and/ or other modifications may bemade without departing from the spirit thereof. Accordingly it isintended that the patent shall cover, by suitable expression in theclaims, the various features of patentable novelty that reside in theinvention.

I claim:

1. In a rolling mill operation a process including the steps ofcollecting coolant water and rolling oil together with lesser quantitiesof tramp oil, stratifying the collection substantially according to thedensity of the components, withdrawing a heavier portion of thestratified collection and subjecting it to a locus of centrifugal force,discharging from adjacent the axis of the locus an oilcontaining portionand from an outer region of the locus a coolant Water discharge for theprocess, withdrawing a lighter portion of the stratified collection,combining it with the oil-containing portion and subjecting it to asecond locus of centrifugal force, withdrawing from adjacent the axis ofthe second locus of centrifugal force a clean rolling oil discharge forthe process, Withdrawing from an outer region of the second locus amixture of water and tramp oil and settling said mixture, withdrawingfrom the settled mixture a lighter portion comprising the tramp oildischarge for the process, and returning at least a portion of the cleanrolling oil discharge for the system to the mill for reuse.

2. A process as described in claim wherein the mixture of Water andtramp oil is Withdrawn through openings in the periphery of the secondlocus, and including the additional steps of withdrawing from thesettled mixture a water component and returning it to the second locusof centrifugal force adjacent the periphery thereof to sate isfy thedemands of the openings so that no rolling oil escapes through theopenings.

3. A process as described in claim 2 wherein the interface in the secondlocus between the oil and the water is adjacent the periphery of thelocus.

References (fitted by the Examiner REUBEN PREEDMAN, Primary Examiner.

SAME-I N. ZAHARNA, Examiner.

1. IN A ROLLING MILL OPERATION A PROCESS INCLUDING THE STEPS OFCOLLECTING COOLANT WATER AND ROLLING OIL TOGETHER WITH LESSER QUANTITIESOF TRAMP OIL, STRATIFYING THE COLLECTION SUBSTANTIALLY ACCORDING TO THEDENSITY OF THE COMPONENTS, WITHDRAWING A HEAVIER PORTION OF THESTRATIFIED COLLECTION AND SUBJECTING IT TO A LOCUS OF CENTRIFUGAL FORCE,DISCHARGING FROM ADJACENT THE AXIS OF THE LOCUS AN OILCONTAINING PORTIONAND FROM AN OUTER REGION OF THE LOCUS A COOLANT WATER DISCHARGE FOR THEPROCESS, WITHDRAWING A LIGHTER PORTION OF THE STRATIFIED COLLECTION,COMBINING IT WITH THE OIL-CONTAINING PORTION AND SUBJECTING IT TO A